1. Field of the Invention
The present invention relates generally to utility pliers and, more particularly, to pliers that self-adjust for applying a grasping force to a workpiece and for augmenting the grasping force applied to the workpiece.
2. Description of the Prior Art
Many types of handheld utility pliers are known in the art. Conventional pliers typically include two plier members interconnected in a scissors-like arrangement allowing for a workpiece to be grasped and compressed by jaw portions of the pliers in response to movement of handle portions of the pliers. Over the years, numerous improvements have been made to the conventional plier design in order to obtain better and more efficient pliers. For example, self-adjusting pliers have been developed in order to provide a set of pliers that more easily and automatically adjust to the size of a given workpiece. However, while such pliers provide adjustment capability, they do not provide active augmentation of clamping force beyond what conventional pliers provide.
A limitation of conventional plier designs is that there is an absolute limit to how close the pivot point can be moved toward the jaws, which also limits the amount of mechanical advantage a user has for applying force to a workpiece. Furthermore, in conventional pliers the handles and jaws are coupled in a fixed relationship, typically using the scissors-like arrangement as described, such that the jaws converge on a workpiece at essentially the same rate as the handles when a user applies hand pressure to the pliers. This type of fixed relationship between the handles, the jaws and the pivot point limits the amount of force that a user can apply to a workpiece and produces an undesirable trade-off between overall handle separation and gripping force being applied to a workpiece. Specifically, the longer the handles the greater the leverage and hence the greater the gripping force that can be applied to the workpiece. However, longer handles are impractical and make use of the pliers more inconvenient because either the handles are too far apart to be conveniently grasped by one hand or, if they are conventionally spaced, the resulting jaw opening is small and limits the range of adjustability of the jaws.
U.S. Pat. No. 5,832,793 discloses an adjustable wrench having a movable handle and a movable jaw for adjusting the wrench to grip objects of various sizes. While this wrench provides some degree of increased mechanical advantage as well as adjustability for grasping variously-sized workpieces, size adjustment is not automatic and requires discrete manipulations using two hands.
U.S. Pat. No. 2,144,180 discloses adjustable pliers where the handles and jaws are arranged other than in the typical scissors-like arrangement. While these pliers do allow for a level of size adjustment, the function is not provided in a seamless, one-handed operation. These particular pliers require a user to re-position his hand for each step of operation.
Many other types of pliers having handles and jaws coupled in a fixed relationship that limits the amount of force that a user can apply to an object are known. For example, U.S. Pat. No. 4,651,598 discloses utility pliers that provide for self-adjustment through employment of a spring-biased control arm positioned between the handles. In this particular hand tool the range of size adjustability within the envelope of acceptable handle spacing is limited because a large portion of the available handle movement is taken up with moving the jaws up against the workpiece from the fully open rest position. This leaves only a minor portion of available handle movement for carrying out the crucial task of workpiece compression. In addition, U.S. Pat. Nos. 3,232,152, 2,906,155 and 1,651,216 disclose adjustable pliers which utilize the concept of shifting pivot points between first and second pivot means positioned at different locations on the pliers. However, these pliers do not include a self-opening feature using spring-biased handles and jaws.
U.S. Pat. No. 5,609,080 discloses another type of pliers which is similar to the well known VISE-GRIP type pliers. Such pliers are typically not considered self-adjusting because they must be initially adjusted to set the opening of the jaws in relation to the workpiece to be grasped.
Other types of pliers are disclosed in U.S. Pat. Nos. 2,375,082, 3,091,841, and 1,639,183. U.S. Pat. No. 2,375,082 provides an adjustable wrench. However, it doesn't provide automatic self-adjustment to the size of a workpiece, nor is it usable with one hand. U.S. Pat. No. 3,091,841 uses a variable leverage linkage between the handles which drives the pivot point toward the jaws when grasping a workpiece. However, this is intended to facilitate expanding snap rings and doesn't provide for force augmentation. The continuous pivot adjustment of these pliers provides variable rate of handle movement compared to jaw movement. However, this is not a two stage approach that provides quick self-adjustment and powerful clamping. U.S. Pat. No. 1,639,183 discloses self-adjusting pliers with no biasing means to move the handles and jaws apart. In addition, while it also relies on two shifting pivots, the two pivot pins are on the same plier member, and the two openings in which the pivot pins move are on the other plier member. These pliers provide no force augmentation above that provided by conventional pliers with a conventional pivot located close to the jaws.
French Patent 2,731,124 discloses self adjustable pliers which utilize a locking mechanism derived from Vise Grip pliers. Like Vise Grip pliers, the hand force applied to the workpiece by the jaws is not linear and proportional to the force being applied to the handles. The force delivered by the jaws ramps up until it peaks as the toggle mechanism moves over center. Also, these pliers don't provide small handle excursion during self-adjustment and large handle excursion during force application. Thus, when these pliers are sized for locking onto large workpieces, they are not particularly easy to grasp by a user with small hands.
There remains a need for improved handheld utility pliers which (1) boost worker safety and productivity by actively augmenting a user's hand strength to lessen the effort and strain of compressing a workpiece, (2) which self-adjust to various workpiece sizes, (3) which provide the capability of applying a greater force to an object being gripped by the pliers, (4) which provide more responsive and precise operation, (5) which can be easily operated by the user, preferably with one hand, and (6) which feature an auditory indication of proper functioning.